1. Field of the Invention
The present invention relates to a cathode-ray tube apparatus.
2. Description of the Related Art
Recently, in a TV receiver and the like, there is a demand for higher image quality along with the increase in size. As one procedure for this, a cathode-ray tube apparatus has been proposed in which a velocity modulation coil is mounted so as to enhance an edge of an image to sharpen image quality. The velocity modulation coil forms a magnetic field in a vertical scanning direction of an electron beam, and changing a scanning velocity in a horizontal scanning direction of the electron beam, thereby enhancing an edge of an image (e.g., see JP 57(1982)-45650 U).
Furthermore, JP 2003-116019 A describes that a pair of ferromagnets are arranged so as to be opposed to each other on an outer circumferential surface of a neck of a funnel in such a manner as to be respectively paired with a pair of loop coils of a velocity modulation coil. According to this configuration, a magnetic field generated by the velocity modulation coil is intensified by the ferromagnets to act on an electron beam concentratedly, so that a velocity modulation effect can be enhanced.
On the other hand, an ordinary color cathode-ray tube apparatus generally includes a deflection yoke and a convergence and purity unit (CPU). The CPU includes a dipole magnet ring, a quadrupole magnet ring, and a hexapole magnet ring for applying a magnetic field to an electron beam, and is attached to an outer circumferential surface of a neck of a funnel in which an electron gun is contained.
In the case of mounting the velocity modulation coil, the ferromagnets for intensifying and concentrating the magnetic field formed by the velocity modulation coil, and the CPU on an outer circumferential surface of a neck of a funnel, conventionally, the ferromagnets are placed in openings of the loop coils of the velocity modulation coil, respectively, and magnet rings of the CPU are placed so as to cover the ferromagnets. Thus, when seen in a direction orthogonal to a tube axis, the ferromagnets and the magnet rings of the CPU are overlapped with each other. Consequently, the magnetic field generated by the magnet rings of the CPU is influenced by the ferromagnets placed inside of the magnet rings to become non-uniform, and the effect of correcting a convergence by the CPU cannot be obtained sufficiently.